Delaying a promise to progress upward in the first post in this series, further work has shown that we need to go sideways a bit. It turns out that according to MODTRAN, like CO2, water does not radiate in the lower troposphere either. We will step through the same sequence with water.

Once again, the red “background run” is looking down and the blue looking up. Similar to CO2, no radiation signal looking down from 1 meter.

Ditto 10 meters.

Again at 100 meters.

At 1 kilometer we began to see a signal in the CO2 bands but nothing equivalent in the water bands. We can note that the up looking signal is dropping to progressively lower temperature or intensity with the lapse rate, particularly in the atmospheric window.

At 5 kilometers we finally get a good signal looking down, but looking up is still stronger.

At 10 kilometers it is getting pretty dry, and except for the lower wave numbers not much is left of the up looking signal.

At 17 kilometers where the atmosphere begins to warm with altitude, little up looking signal is left.

At 40 kilometers the up signal is done. The down looking signal records the entire water spectrum radiating mightily to space at 329 watts per square meter. The solar radiation at the top of the atmosphere is measured at 340 watts per square meter. Without bothering to radiate significantly in the first 5 kilometers of the atmosphere, water still manages to radiate away 97% of the planet’s incoming energy.